The present invention relates to an air conditioner for exchanging heat with a refrigerant so as to adjust a room temperature to a designated temperature and for shifting a designated temperature to a predetermined temperature under a predetermined condition when a user is sleeping.
An air conditioner has a compressor for compressing a refrigerant it executes a refrigerating cycle during which it exchanges heat with the refrigerant so as to execute a controlled operation for causing the room temperature to approach the designated temperature.
A conventional air conditioner performs the following control operation for causing the room temperature to approach the designated temperature: The air conditioner performs a fuzzy operation corresponding to the difference .DELTA.t between the designated temperature and the room temperature, and the variation thereof. It also calculates an increase/decrease in the frequency controlling an AC motor of a compressor. Corresponding to the increase/decrease in the frequency, the air conditioner increases or decreases the operation power of the AC motor so as to cause the room temperature to asymptotically approach the designated temperature. In addition, the air conditioner compensates the real operation power for various factors, such as the current consumption, the temperature of the compressor, and the outside temperature at that time.
However, when the air conditioner performs the control operation while the user is sleeping, due to the fact that the body temperature of the user decreases while he is sleeping, it cannot provide the user with a comfortable sleeping environment. In other words, the user designates a temperature while he is awake, not a temperature while he is sleeping. When the body temperature of the user decreases while he is sleeping, he feels too cold in a cooling mode of the air conditioner and too hot in a heating mode.
To solve such a problem, when a conventional air conditioner determines that the room temperature accords with the designated temperature, it increases the designated temperature to a predetermined temperature when in the cooling mode and decreases the designated temperature to another predetermined temperature in the heating mode so as to handle a desirable temperature change during sleeping.
It takes a long time until the room temperature reaches a designated temperature. Thus, the room temperature does not easily accord with the designated temperature. Consequently, it is very difficult to determine whether the room temperature accords with the desired temperature. When the room temperature approaches a predetermined range of the desired temperature, the air conditioner determines that the room temperature accords with the desired temperature and performs the above-described temperature shift control.
However, when the amount of the load of the air conditioner is balanced with the operating power, the air conditioner tries to converge to the balanced state. In other words, the air conditioner stably operates in the condition that the room temperature does not accord with the designated temperature. In this case, the air conditioner does not perform the above-described temperature shift control. Thus, the air conditioner cannot provide the user with a temperature corresponding to his decreased body temperature.